Fine-needle aspiration biopsies of metastatic neuroendocrine tumors in liver: Use of transmission electron microscopy and protein A gold technique in diagnosis

Five fine‐needle aspiration biopsies of liver were studied to evaluate the use of electron microscopy and protein A gold technique in the diagnosis of metastatic neuroendocrine tumors. All five cases had cytologic features suggestive of neuroendocrine tumors and neurosecretory granules on ultrastructural examination. The aspirates were stained by the immunoperoxidase technique and the postembedding protein A gold technique using the antibody to chromogranin A. Three cases were positive for chromogranin A by both immunoperoxidase and protein A gold techniques. Two cases were positive by protein A gold technique and negative by immunoperoxidase technique. Confirmation of neurosecretory granules by immunochemistry is ideal, since ultrastructurally they can be mimicked by other electron‐dense inclusions. Advantage of the protein A gold technique is the use of the same material for both ultrastructural evaluation and the protein A gold technique.